This investigation is designed to elucidate metabolic and structural influences on the ability of cholesterol and other sterols to act as architectural components of membranes. This will be achieved through studies of the biosynthetic mechanisms of alkylation, dealkylation, and reduction by which the structure of the steroidal side chain is determined, through an examination of the relationship between structure and occurrence in subcellular particles, and an exploration of ways to substitute one sterol for another in the myelin sheath. In addition, the mechanism of action of inhibitors of sterol biosynthesis will be investigated.